1. Field of the Invention
The present invention relates to a battery including a nonaqueous electrolytic secondary battery.
2. Description of the Related Art
A battery such as a nonaqueous electrolytic secondary battery includes a positive current collector and a negative current collector for electrically connecting a positive electrode and a negative electrode in an electrode assembly contained inside of a battery case to a positive external terminal and a negative external terminal, respectively. A base of the current collector is fixed to a cover for sealing an upper opening of the battery case by means such as caulking using, for example, a rivet. A lower gasket for securing sealability or the like is interposed between the base of the current collector and a lower surface of the cover (see Japanese Unexamined Patent Application Publication No. 2003-346882 (FIG. 1)).
The higher the occupancy of an electrode assembly with respect to the volume of a battery case, the higher the energy density. Consequently, from the viewpoint of energy efficiency, it is preferable that the upper end of the electrode assembly should be disposed as proximately to the lower surface of a cover as possible. However, when the lower gasket formed into a substantially merely flat plate disclosed in Japanese Unexamined Patent Application Publication No. 2003-346882 is disposed at the lower surface of the cover, the upper end of the electrode assembly cannot be disposed sufficiently proximately to the lower surface of the cover, and therefore, a high energy density cannot be achieved. Moreover, the flat cover and the flat lower gasket are brought into mere contact with each other on the plane, and therefore, the gasket is liable to be rotated. The rotation of the gasket exerts a load on a portion where an external terminal and a current collector are electrically connected to each other (e.g., a portion caulked and joined by a rivet).